256 vs 447 motor differences

Mailman

Hardly a Guru
Top Contributor
Messages
9,834
Reaction score
47,514
Points
688
Location
Surprise Az
So I think I’ve been laboring under a couple of false assumptions, if anyone could clarify a couple things for me I would appreciate it. I always thought there were just the two factory motors, the 256 and the 447,
but according to this post there are four? My ‘72 since it has a crank with a starter gear makes my motor a 306?
And a 533, I never even heard of. Never mind the rephase motors, I get that.
C4EA4D20-8B33-4793-A1CF-5DBB126A8A9A.jpeg


Here is another thing I’ve apparently misunderstood. I knew the 256 motors had longer rods, so I thought they also had a longer stroke, although now that I’m thinking this through, the stroke wouldn’t change, only the cylinder volume. Anyways according to this, all motors have the same stroke.

B3DBD354-45FD-4E14-9C36-264F04E5271E.jpeg


So what I’m wondering, if the stroke is the same and the crank is the same 360 degrees, then is the only difference between the motors , the cam profile? Because my XS2 and my 77D feel completely different.
Are there any other fundamental differences?
 
“Do not meddle in the affairs of wizards Yamaha Engineers, for they are subtle and quick to anger.”
The length of the rod is compensated, like 2many sez, by the height of the wrist pin in the piston.
 
Last edited:
Honestly I think Yamaha had to adjust the power output and horsepower curve to match rider's expectations from a 4 stroke motor. With such a strong 2 stroke background they designed and tuned a rather peaky revver of a 4 stroke then tried to sell it to British bike enthusiasts, and American big iron drivers, used to low RPM stump pullers. They were limited by basic design but changed details to lower and broaden the powerband. But you can't exactly ADVERTISE this years model, now makes less power...


“Do not meddle in the affairs of dragons for you are crunchy and taste good with ketchup.”
 
Honestly I think Yamaha had to adjust the power output and horsepower curve to match rider's expectations from a 4 stroke motor. With such a strong 2 stroke background they designed and tuned a rather peaky revver of a 4 stroke then tried to sell it to British bike enthusiasts, and American big iron drivers, used to low RPM stump pullers. They were limited by basic design but changed details to lower and broaden the powerband. But you can't exactly ADVERTISE this years model, now makes less power...


“Do not meddle in the affairs of dragons for you are crunchy and taste good with ketchup.”

Ahhh...Haha! You are cracking me up! :laugh2:

Hey, as long as I’m asking random questions, anyone know what ignition this is? I ran across this photo the other day.
37F80EDB-46BD-4C51-8C34-93A835AC1238.jpeg
 
So I think I’ve been laboring under a couple of false assumptions, if anyone could clarify a couple things for me I would appreciate it. I always thought there were just the two factory motors, the 256 and the 447,
but according to this post there are four? My ‘72 since it has a crank with a starter gear makes my motor a 306?
And a 533, I never even heard of. Never mind the rephase motors, I get that.
View attachment 156999

Here is another thing I’ve apparently misunderstood. I knew the 256 motors had longer rods, so I thought they also had a longer stroke, although now that I’m thinking this through, the stroke wouldn’t change, only the cylinder volume. Anyways according to this, all motors have the same stroke.

View attachment 157000

So what I’m wondering, if the stroke is the same and the crank is the same 360 degrees, then is the only difference between the motors , the cam profile? Because my XS2 and my 77D feel completely different.
Are there any other fundamental differences?
The XS1s (256) sported a different head, intake port with semi flat floor with short turn corners cut down, different combustion chamber, different bowl shaping and cam. A longer rod, like rephasing, shifts the power band to the upper end with a slight torque reduction due to pumping loses(PULL) through the intake port. The Europeans got lucky being handed the 533 while we got screwed but they have longer winding roads,they just ride differently.
 
I can't answer your question Bob... I'm no expert on XS lineage, but there's other factors. Gearing (and tire size) can make a huge difference in feel. The heads... not all casting are created equal. Some are cleaner than others. Carbs.... even on identical engines, can "feel" different. In the age of computer controlled engines we tend to forget that carbs are always a compromise. They have to transition between pilot, needle and main jets... with overlaps 'tween 'em. If you were to graph out a mixture line from idle to full throttle, a computer can be programed to nail that line. Carbs... not so much. As you transition from one jet to the other, you're gonna go lean or rich above and below that line. The better you dial in the carbs, the closer you'll follow the line, but even identical carbs will have variations from manufacturing.
When I was a kid, there were these twins I hung out with. Daddy was rich and bought 'em 2 brand new CB350's (1970-71 ish). They were even within a handful of serial #'s from each other. One was quiet a bit faster than the other... to the point that they took it in to have it checked.
Yup, the good ol' days before computers and CNC's. Btw... my wore out YR3 would smoke both of 'em. ;)
 
I can't answer your question Bob... I'm no expert on XS lineage, but there's other factors. Gearing (and tire size) can make a huge difference in feel. The heads... not all casting are created equal. Some are cleaner than others. Carbs.... even on identical engines, can "feel" different. In the age of computer controlled engines we tend to forget that carbs are always a compromise. They have to transition between pilot, needle and main jets... with overlaps 'tween 'em. If you were to graph out a mixture line from idle to full throttle, a computer can be programed to nail that line. Carbs... not so much. As you transition from one jet to the other, you're gonna go lean or rich above and below that line. The better you dial in the carbs, the closer you'll follow the line, but even identical carbs will have variations from manufacturing.
When I was a kid, there were these twins I hung out with. Daddy was rich and bought 'em 2 brand new CB350's (1970-71 ish). They were even within a handful of serial #'s from each other. One was quiet a bit faster than the other... to the point that they took it in to have it checked.
Yup, the good ol' days before computers and CNC's. Btw... my wore out YR3 would smoke both of 'em. ;)

Yeah, that certainly seems reasonable. There are a lot of variables.
 
If my memory serves me well, witch it probably doesn’t, the 75XS I have now is considerably smoother than the XS2 I had in 73. Having said that I don’t ride at the speeds I used to, I’m a bimbler now.
As with all early model vehicles the initial models are refined, improved, get slower, until unrecognisable, the XS lineage is clear to see from first to last but, the later bikes are more refined, in my opinion.
 
The XS1s (256) sported a different head, intake port with semi flat floor with short turn corners cut down, different combustion chamber, different bowl shaping and cam. A longer rod, like rephasing, shifts the power band to the upper end with a slight torque reduction due to pumping loses(PULL) through the intake port. The Europeans got lucky being handed the 533 while we got screwed but they have longer winding roads,they just ride differently.
I noticed a small blue thing in front of the spark plug. Any idea what it is?
 
In what way?

The 77 is much smoother and as Rasputin said it just feels more refined, it has a one tooth smaller rear sprocket, which makes some difference, but it is a much more comfortable bike at speed. However my XS2 feels more exciting. The exhaust note and the throbbing vibrations just make it feel eager.
 
Back
Top